1. Field of the Invention
The present invention relates to Third Generation (3G) cellular telecommunications systems, and in particular to a method and system for Multi-Protocol Label Switching (MPLS) based data flow aggregation in a 3rd Generation (3G) cellular telecommunications system.
2. Description of the Related Art
UMTS (Universal Mobile Telecommunications Service) is a Third-Generation (3G), broadband, packet-based transmission of text, digitized voice, video, and multimedia at data rates up to 2 Megabits per second (Mbps) that offers a consistent set of services to mobile computer and phone users independently of their location in the world. Based on the Global System for Mobile (Global System for Mobile communication) communication standard, UMTS, endorsed by major standards bodies and manufacturers, is the planned standard for mobile users around the world. With UTMS, computer and phone users are constantly attached to the Internet as they travel and, through the roaming service, have the same set of capabilities no matter where they go. Especially at the beginning of UMTS deployment, users can have multi-mode mobile devices that switch to the locally available technology (such as GSM 900 and 1800) where UMTS is not yet available.
Today's cellular telephone systems are mainly circuit-switched, with connections always dependent on circuit availability. Packet-switched connection, using the Internet Protocol (IP) will also make possible to provide new services, such as alternative billing methods (pay-per-bit, pay-per-session, flat rate, asymmetric bandwidth, and others). The higher bandwidth of UMTS also promises new services, such as video conferencing. UMTS promises to realize the Virtual Home Environment in which a roaming user can have the same services to which the user is accustomed when at home or in the office, through a combination of transparent terrestrial and satellite connections.
UMTS is also planned to revolutionize operators network with better frequency efficiency and lower transport costs by utilizing Asynchronous Transfer Mode (ATM) communications for both voice and data services, as defined for example in the Technical Specification Group Services and System Aspects; Release 1999 Specifications: 3rd Generation Partnership Project, 3GPP TS 21.101 version 3.7.0, herein included by reference. UMTS is based on the General Packet Radio Service (GPRS) core networking with its seamless high-speed delivery of data for point-to-point applications, which allows innovative services to be created. However, GPRS uses GPRS Tunnelling Protocol (GTP) to forward packets from the GGSNs (GPRS Gateway Service Nodes) to the SGSNs (Serving GPRS Service Nodes) in order to reach a mobile device, dynamically setting up communication tunnels between the GGSN and the mobile unit home network, and allowing the mobile unit to have its home network served beyond the GGSN Internet Gateway. But GTP is deficient in terms of session set-up and hand-off response time because of its complex plurality of primitives involved, as well as in terms of sessions' reliability due to the non-negligible probability of data routing failure during the communications sessions.
GTP includes both signalling (GTP-C for the Control Plane) and data payload (GTP-U for the Data Plane) transfer procedures. In the signalling plane, GTP-C specifies a tunnel control and management protocol that allows the SGSN to provide GPRS services for a mobile station with signalling that creates, modifies and deletes communications tunnels. For that purpose, the User Datagram Protocol (UDP) is used as the protocol for transferring signalling messages between GPRS service nodes. In the transmission plane, GTP-U uses a tunnelling mechanism to carry user data packets. The whole specification for GTP can be found in the Release 1999 Specifications: 3rd Generation Partnership Project, 3GPP—Technical Specification TS29.060, General Packet Radio Service (GPRS); GPRS Tunneling Protocol across the Gn and Gp interface, herein included by reference.
Reference is now made to FIG. 1 (Prior Art), which shows a high-level reference model diagram of a prior art Third Generation IP (3G.IP) cellular telecommunications system 10. Terminal Equipment (TE) 12 and Mobile Terminals (MTs) 14 communicate via the UMTS Radio Access Network (UTRAN) 16 and/or the Enhanced Datarate for GSM Evolution (EDGE) Radio Access network (ERAN) 18 with an Enhanced SGSN (ESGSN) 20 of the system 10. The ESGSN 20 provides the direct access point for the terminals 12 and 14, and is connected via a Gn interface 22 to at least one Enhanced GGSN (EGGSN) 24 that provides the gateway to SGSN across mobile networks that the users may visit. The GGSN 24 is also the access point for other packet data networks 26 and 28, allowing someone to, for instance, send an email from a (fixed network) PC to someone with a GPRS phone. Other nodes are as well illustrated in FIG. 1, although for simplification purposes their function is not described herein. It will be however understood by those skilled in the art that these nodes are those described in the Third Generation Partnership Project (3GPP) Technical Specification 3GPP TS 23.002, V3.5.0, Network Architecture, herein included by reference. The Gn interface 22 uses GTP tunnelling to forward packets from EGGSN 24 to ESGSN 20 to reach a mobile device, dynamically setting up tunnels between GGSN and its home network and allowing the mobile unit to have its home network served beyond the GGSN Internet Gateway. However, it is recognized that, for example, the Gn interface lacks reliability in supporting continuous data sessions, i.e. it happens that IP routers 30 of the Gn interface 22 responsible for transmitting the data flow between the ESGSN 20 and the EGGSN 24 may experience failures for various reasons. When these malfunctions occur, it was realized that it may take up to 90 seconds for a fail over router to effectively take over and successfully redirect the same communication.
Also detrimental to the normal operation of GPRS-based networks is the transfer of user data packets during a mobile terminal hand-off (intra or inter GGSN). Reference is now made to FIG. 2 (Prior Art), which shows an exemplary high-level network diagram of an existing GPRS network 50, wherein a Mobile Terminal (MT) 52 is provided packets switched cellular service via a Base Station 1 (BS 1) 54, connected to a Radio Network Controller (RNC) 56, which is itself connected to an SGSN-A 58. The packet data of the data session carried on by the MT 52 is transported via the GTP tunnel 60 established between the SGSN-A 58 and the GGSN 62. In current implementations, when the user equipment 52 is handed-off from the routing area served by the SGSN-A 58 to another routing area served by another SGSN, such as for example by the SGSN-B 64, a new GTP tunnel 66 must be established between the GGSN 62 and the target SGSN-B 64. In such a case, in existing GPRS networks, the switching between GTP tunnels, for instance, requires user data packets to be kept in a queue for typically 0.5 to 5 seconds before the switch becomes effective from the old GTP tunnel 60 to the new GTP tunnel 66. It is therefore difficult to contemplate sending time sensitive traffic, such as voice traffic and video conferencing traffic over the current GPRS systems, when traffic encounters core network delays (excluding IP-Backbone delay) well over 500-5000 ms.
Although there is no prior art solution as the one proposed hereinafter for solving the above-mentioned deficiencies, the Multi Protocol Label Switching (MPLS) technology, described in the request for Comments RFC 3031, bears some relation with the field of the present invention, by aiming at achieving fast and simple forwarding of IP traffic. In MPLS, routing information is signalled between neighbouring nodes and a group of virtual paths known as Label Switched Paths (LSP) are established between the edges of the MPLS network. In MPLS, a packet flow is classified or labelled by an MPLS network's entry node onto an LSP that will adequately direct the packet flow towards the exit node, and will also forward the packet data flow toward the destination. Each MPLS node that participates in the LSP is known as a Label Switched Router (LSR). Each LSR along the LSP has an incoming and outgoing labels binding that represent the routing information at each LSR and indicate the forwarding direction as well as forwarding behaviour to be applied to the packet flow. The incoming and outgoing labels for each LSR therefore act as shorthand for routing, and are pre-signalled between neighbouring nodes through special protocols such as Label Distribution Protocol (LDP) [RFC 3036]. LSR packet flow forwarding in that scenario becomes a simple label lookup and swapping (changing incoming to outgoing labels) operations, rather than best prefix match as in traditional routing. When the packet flow reaches the exit node of the MPLS network, the packet flow is unlabelled and forwarded toward the destination point.
Some extensions to existing routing protocols have been proposed to enable explicit routing in MPLS networks such as traffic engineering extensions to RSVP (RSVP-TE) and Constraint Routing LDP (CR-LDP). The main goal of explicit routing is to have only one destination for each entering packet bringing the logic of path establishment to the network's edges. Packets are classified at the edge into their explicit path and do not need to carry the explicit routing information as in traditional IP networks. Those extensions fill the objective of traffic engineering to avoid over-utilizing certain paths for traffic forwarding while other paths in the network remain under-utilized.
While MPLS simplifies forwarding of IP data, it does not provide QoS. In fact, MPLS nodes do not take any QoS parameters into account for the forwarding of packets, but rather interpret each packet's label to forward it accordingly.
Accordingly, it should be readily appreciated that in order to overcome the deficiencies and shortcomings of the existing solutions, it would be advantageous to have a method and system for effectively supporting data communications in a GPRS/UMTS cellular telecommunications network. The present invention provides such a method and system.